Sally Alicia Acorn (voiced by Kath Soucie) is the co-star of the series, but is also Sonic's love interest later girlfriend, the head leader of the Knothole Freedom Fighters, a mother figure to Tails, best friend to Bunnie, co-archenemy to Dr. Robotnik, the tomboyishly beautiful daughter of King Acorn and the crown princess of Mobius. Her species is a chipmunk, which is a subspecies of a ground squirrel. She often accompanies the Freedom Fighters on field missions in Robotropolis and uses her portable computer, NICOLE, to access Robotnik's files. Despite how Sonic normally annoys her, she still loves him.

Despite being very stressed out a lot, Sally is a kind a caring girl with a huge heart. She isn't the person to give up on anyone. Especially her boyfriend Sonic, even if he may act childish. He was her first friend since childhood. And they are both rather loyal to each other. While Sonic has the more chill and "cool dude" personality, Sally has a more stressed out, strong leader and smart and sassy personality despite her beauty.